Got a bit of a problem, just been out in my car, happily going along making a bar of boost, came off a roundabout in 2nd, changed to 3rd and I have no boost at all, the car is driveable, just, but has absolutely no power.

All the boost hoses are on, none are split, there were no funny noises, bangs or clunks, it just now has no power.

What could be the problem?